I have a good friend I've known since infant school - over 35 years. Our friendship has waxed and waned over the years as you might expect but I do consider her one of my closest friends and vv.
About 12 years ago she started dating someone. She moved in with him a few months later. I was always a little 
about him, he is very very tight with money (which is a characteristic I find particularly unattractive) a commitment phobic, and it's always seemed very one way - he has lots of hobbies which she joins in with, but he never does the same for her. She had the marriage and babies conversation with him many times. The last time, about 5 years ago, he said he wasn't ready, wasn't sure if he ever would be, BUT that he loved her and wanted to be with her. So they stayed together - although she wanted marriage and a family, she wanted to be with him more, so was prepared to accept the rest of it might not happen.
3.5 years ago he had a 'milestone' birthday, she threw him a big surprise party. Despite what she'd said I think that she hoped this would be the decider for him - that it would compel him to make a decision and 'commit' to her. It didn't - in fact he barely even thanked her and was totally unappreciative of the effort she'd made.
A year later - so 2.5 years ago now - he said he felt they'd come to the end of the road, she wasn't independent enough, he was fed up of his house being full of her stuff (they are both chronic hoarders, she also shops constantly) and he wanted their relationship to end.
So she got a flat of her own (which is now full - literally, you can barely get in the door - with her stuff). She stays there one day a week, the rest of the time she spends with him. Still sharing a bed, cooking his dinner etc. Just like nothing has happened.
Meanwhile he has been on dating sites for the last 6 months, has lots of girls as 'friends' on his FB, and regularly stays out all night.
I have said to her as nicely as I can that she needs to cut her ties with him, this dragging it out for over 2 years is not at all healthy. He's never attempted to throw her out but I suspect it's only a matter of time especially now he's dating other people :(
I've offered to help her move the last of her stuff out of his, and to spend weekends with her so she's not on her own. She knows she is welcome at mine anytime. I've asked her if there's anything else I can do, she says only that she's not ready to finish it :( I really can't see what more I can do but would welcome opinions.